Sensing brain activity

The NV center in diamond behaves like an artificial atom trapped in the diamond crystal with a position controlled at the nanometer scale. Its spin state can be optically polarized and coherently manipulated at room temperature and it can be optically detected. This results in a quantum sensor with extreme sensitivity and nanometer scale spatial resolution.
There are numerous sensing applications of NV centers. The most advanced ones measure magnetic fields, but they can also use measure electric field, temperature or pressure. Here we have chosen three applications in the fields of data storage, biology and spintronics.

The generation and control of fast switchable magnetic fields with large gradients on the nanoscale is of fundamental interest in material science and for a wide range of applications. However, it has not yet been possible to characterize those fields at high bandwidth with arbitrary orientations. Here, we measured the magnetic field generated by a hard-disk-drive write head with high spatial resolution and large bandwidth by coherent control of single electron and nuclear spins. This method paves the way for precision measurement of the magnetic fields of nanoscale write heads, which is important for future miniaturization of these devices. – Publication: Jakobi et al., Nature Nanotechnology 12, 67-72 (2017).

A sensor, consisting of two quantum bits corresponding to an electronic spin and an ancillary nuclear spin, is used to demonstrate room temperature magnetic resonance detection and spectroscopy of multiple nuclear species within individual ubiquitin proteins attached to the diamond surface. Using quantum logic to improve readout fidelity and a surface treatment technique to extend the spin coherence time of shallow NV centers, we demonstrate magnetic field sensitivity sufficient to detect individual proton spins within one second of integration and we observe spectral features that reveal information about the chemical composition of the molecule. –Publication: Lovchinsky et al., Science 351, 836-841 (2016).

Nearly 90% of known magnetic materials have dominant antiferromagnetic interactions, resulting in no or very small magnetization, and most are also insulators. This strongly impedes their investigation, especially when the magnetic order needs to be mapped at the nanoscale
Scanning-NV magnetometry has shown to be ideally suited to investigate complex antiferromagnetic orders at the nanoscale through (i) the first real-space visualization of a cycloidal antiferromagnetic order in a thin film of bismuth ferrite BiFeO3 and (ii) imaging of individual nanoscale AF domains in a thin film of chromium oxide Cr2O3 across the paramagnet-antiferromagnet phase transition. These results might have an important impact in the emerging field of antiferromagnetic spintronics. – Publication: Gross et al., Nature 549, 252 (2017).